Atazanavir (ATV) has already been considered as a potential repurposing drug to 2019 coronavirus disease (COVID-19); however, there are controversial reports on its mechanism of action and effectiveness as anti-severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Through the pre-clinical chain of experiments: enzymatic, molecular docking, cell-based and in vivo assays, it is demonstrated here that both SARS-CoV-2 B.1 lineage and variant of concern gamma are susceptible to this antiretroviral. Enzymatic assays and molecular docking calculations showed that SARS-CoV-2 main protease (M^pro) was inhibited by ATV, with Morrison’s inhibitory constant (K_i) 1.5-fold higher than GC376 (a positive control) dependent of the catalytic water (H₂O_cat) content. ATV was a competitive inhibitor, increasing the M^pro’s Michaelis–Menten (K_m) more than sixfold. Cell-based assays indicated that different lineages of SARS-CoV-2 is susceptible to ATV. Using oral administration of ATV in mice to reach plasmatic exposure similar to humans, transgenic mice expression in human angiotensin converting enzyme 2 (K18-hACE2) were partially protected against lethal challenge with SARS-CoV-2 gamma. Moreover, less cell death and inflammation were observed in the lung from infected and treated mice. Our studies may contribute to a better comprehension of the M^pro/ATV interaction, which could pave the way to the development of specific inhibitors of this viral protease.

Coronavirus disease 2019 (COVID-19) still causes death in elderly and immunocompromised individuals, for whom the sustainability of the vaccine response may be limited. Antiviral treatments, such as remdesivir or molnupiravir, have demonstrated limited clinical efficacy. Nirmatrelvir, an acute respiratory syndrome coronavirus 2 (SARS-CoV-2) major protease inhibitor, is clinically effective but has been associated with viral rebound and antiviral resistance. It is thus necessary to study novel and repurposed antivirals for the treatment of COVID-19. We previously demonstrated that daclatasvir (DCV), an inhibitor of the hepatitis C virus (HCV) NS5A protein, impairs SARS-CoV-2 replication by targeting viral RNA polymerase and exonuclease, but the doses of DCV used to inhibit the new coronavirus are greater than the standard human plasma exposure for hepatitis C. Because any potential use of DCV against SARS-CoV-2 would be shorter than that reported here and short-term toxicological studies on DCV show that higher doses are tolerable, we searched for doses of DCV that could protect transgenic mice expressing the human ACE2 receptor (K18-hACE-2) from lethal challenge with SARS-CoV-2. We found that a dose of 60 mg/kg/day provides this protection by reducing virus replication and virus-induced lung insult. This dose is tolerable in different animal models. Taken together, our data provide preclinical evidence that can support phase I clinical trials to confirm the safety, tolerability, and pharmacokinetics of new doses of daclatasvir for a short duration in humans to further advance this compound’s utility against COVID-19.

Malaria remains a major global health burden, especially in children under the age of five. Pediatric treatment often requires tablet fragmentation for its dose adjustment according to body weight, which intensifies bitterness and may reduce treatment adherence. Complexation of bitter-tasting drugs with ion-exchange resins for taste masking is a promising strategy to improve palatability. Here, we evaluated whether a chloroquine–resin complex (CLQ-R) preserves the pharmacokinetic profile and antimalarial efficacy of chloroquine diphosphate (CLQ) while masking its bitter taste. CLQ-R was prepared at a 1:1 (w/w) drug-to-resin ratio using polacrilin potassium (Amberlite IRP88). The in vitro antimalarial activity of CLQ-R was assessed using Plasmodium falciparum 3D7 strain, and the parasite proliferation was determined by SYBR Green DNA-staining. CLQ plasma concentrations and mice biochemical parameters were evaluated following oral administration of CLQ or CLQ-R. The in vivo antimalarial activity was evaluated in P. berghei ANKA–infected C57BL/6 mice using the four-day suppressive and recrudescence tests, with parasitemia assessed by flow cytometry. Taste perception was determined by 48-hour two-bottle preference test. CLQ-R displayed similar plasma concentration and biochemical profiles to CLQ. CLQ-R was able to maintain a strong in vitro antimalarial activity with IC50 of 30 nM with minimal hemolytic activity and reduced in vivo parasitemia by >95%. Notably, mice exhibited a 15.5% higher preference for CLQ-R, indicating improved palatability. These findings demonstrate that CLQ-R preserves CLQ pharmacological activity while masking its bitter taste, supporting its potential as a pediatric-friendly antimalarial formulation.